The present invention relates to a base station transmission power control method and apparatus which control the transmission power of a base station from a potable terminal apparatus.
A potable terminal apparatus based on the W-CDMA (Wideband-Code Division Multiple Access) scheme has a transmission power control function of controlling transmission power from a base station. According to this function, reception quality as a reference is set in a potable terminal apparatus in advance, and the transmission power of a base station is so controlled as to satisfy the quality requirement. A block error rate (to be referred to as a BLER hereinafter) is a parameter used for reception quality.
A conventional base station transmission power control algorithm will be described with reference to FIG. 4. According to the conventional method, an expected value x of a BLER is set in advance as reception quality required for each service in a potable terminal apparatus (step S1).
When a communication channel is opened, the potable terminal apparatus performs a CRC (Cyclic Redundancy Check) computation on the basis of reception data. This CRC computation result is counted m (m is an integer equal to or more than 1) times (step S2). In this case, if x=10−4 is set, the CRC computation result must be counted at least m=1000 times. Upon counting the CRC computation result m times, the potable terminal apparatus calculates a BLER.
The potable terminal apparatus then compares the calculated BLER with the expected value x (step S3). If the BLER is larger than the expected value x (the reception state is worse than the state represented by the expected value), the potable terminal apparatus sends, to the base station, a transmission power control (to be referred to as TPC) bit for increasing the transmission power of the base station by a designated transmission power increase amount (step width) λ (step S5). If the BLER is equal to or smaller than the expected value x (the reception state is better than the state represented by the expected value), the potable terminal apparatus sends, to the base station, a TPC bit for decreasing the transmission power of the base station by a designated transmission power decrease amount (step width) γ (step S7). With this operation, transmission power control on the base station can be performed. The designated transmission power decrease amount (λ, γ) is written in the specifications “25,214 Physical layer procedure (FDD) Section 5” defined by the standardization initiative called the 3GPP (Third Generation Partnership Project).
A BLER is a parameter calculated at intervals of several msec to several ten msec (e.g., 10 msec, 20 msec, or 40 msec). In general, a value of about 10−4 is used as an expected value of a BLER set as reception quality. According to the conventional transmission power control method, therefore, to satisfy BLER=10−4, measurement must be continued for at least 100×N sec (10 msec×N÷10−4). It takes much time to measure a BLER. Note that N (integer) represents a TrCH (transport channel) size.
A measurement time of 100×N sec for a BLER is considerably long as compared with the minimum value of the intervals of execution of transmission power control. For this reason, a considerably long period of time is required for transmission power control (improvement in reception quality). To execute accurate transmission power control at high speed, it is required to shorten the measurement time for a BLER.